Disposition and interpatient variability have been evaluated in 80 febrile, granulocytopenic cancer patients who were being treated with a third generation cephalosporin - ceftazidime. Disposition in cancer population appears to be significantly different than that observed in normal volunteers. The half-life of drug elimination appears to be 2 fold that of normals (3.7 vs. 1.8 hr.). In 44 episodes of FUO, treatment success with ceftazidime alone was 75% while in 30 episodes of DI the success was 52%. Overall treatment success in the study exceeded 90% upon addition of an antifungal agent. Clinical outcome under the treatment protocol was excellent. We are attempting to correlate the minimum inhibitory concentration of isolates with the trough levels of ceftazidime observed in these patients in order to provide therapeutically desired plasma ceftazidime concentration which will lead to a therapeutic success. Variability in peak and through levels suggests that although not recommended by the manufacturer, dosage modifications may be necessary in this group of patients in order to minimize potential toxicity and cost to the patient. Distribution of several pharmacokinetic parameters appears to be binomial.